Misuse of span in sentences

[cconcolato]

A small error was introduced in #318. In 10.4, the current text says:

The implicit duration of an anonymous span, a set element, or a span element whose children are exclusively text nodes, is defined as follows: if the span's parent time container is a parallel time container, then the implicit duration is equivalent to the indefinite duration value as defined by [SMIL 2.1]; if the span's parent time container is a sequential time container, then the implicit duration is equivalent to zero.

This is wrong as this applies to <set> elements. I propose to remove "span's" (twice).

[palemieux]

Good catch.

[nigelmegitt]

Hah, I spotted this and commented on it at w3c/ttml2#603 (comment) before I realised you'd opened this issue @cconcolato ! (I'm playing catch-up...) I agree with the proposal.